Non-insulin-dependent or type 2 diabetes mellitus is a metabolic disease characterized by an elevated blood glucose concentration that results from inadequate insulin action in insulin-sensitive tissues and from abnormal insulin secretion. In the USA, Europe and most westernized countries, type 2 diabetes affects approximately 6% of the population. It is estimated that by 2010, >220 million people worldwide will be affected by the disease, promoted by a dramatic increase in the incidence of obesity and a sedentary lifestyle. To achieve glucose control and prevent diabetic complications (retinopathy, cardiovascular disease, and nephropathy, among others), patients currently receive therapeutic agents that have limited efficacy and are associated with side effects. Thus, there is a need to develop more efficient therapeutic agents. Our long-term goal is to identify genes that can be targeted with drugs to improve the treatment of type 2 diabetes. Current technologies to validate the role of genes in disease involve the development of animal models with null alleles for the target gene. In some instances, absence of a gene is incompatible with normal development, leading to death in utero. In addition, certain studies need to knockdown gene function in an adult animal. The objective of the present proposal is to develop a system to downregulate gene expression in liver. We will target a gene involved in fatty acid production, Srebp-1, expression of which is upregulated in type 2 diabetes. Our goals will be accomplished by administration of a recombinant gutless adenovirus expressing a small interfering RNA (siRNA) to reduce mRNA levels. The siRNA technology has emerged as a new tool to study gene function by inducing posttranscriptional gene silencing. We expect that the objective of this proposal will be achieved by pursuing the following specific aims: (i) Establish the optimal conditions to achieve complete Srebp-1 gene silencing in liver (ii) Determine the feasibility of expressing a siRNA molecule in the liver of an adult animal for multiple months and (iii) validate the siRNA expression system as a tool to study gene function in an animal model of disease. The work proposed in this application is significant because it will provide a novel tool to study the effects of gene silencing in liver. Upon completion of our studies, the system could be used in a large number of research applications directed at studying gene function in this organ as well as many other tissues that can be transduced by adenoviral vectors.